Advertise the maximum offset the .adjphase callback is capable of
supporting in nanoseconds for IDT devices.

Refactor the negation of the offset stored in the register to be after the
boundary check of the offset value rather than before. Boundary check based
on the intended value rather than its device-specific representation.
Depend on ptp_clock_adjtime for handling out-of-range offsets.
ptp_clock_adjtime returns -ERANGE instead of clamping out-of-range offsets.

Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Min Li <min.li.xe@renesas.com>
Signed-off-by: Rahul Rameshbabu <rrameshbabu@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>